The present invention relates to a bus system using a multi-slot connector. More particularly, the present invention relates to a multi-slot connector having an integrated bus which connects a plurality of modules in a bus system.
Contemporary bus systems provide for the daisy chain connection of multiple modules on a motherboard. A conventional topology for connecting multiple modules is conceptually illustrated in FIG. 1A. In this example, one or more connectors 11 are mounted on a motherboard 10. Each connector 11 is adapted to hold a module 13. Within this arrangement, modules 13 are sometimes termed "daughterboards" since each commonly holds one or more integrated circuits 14.
In many contemporary bus systems, a bus runs between a controller 12 and a bus termination impedance 15. The bus typically comprises multiple signal lines communicating data and/or control information between the controller and one or more of the integrated circuits on one or more of modules 13. Controller 12 may take many forms including a microprocessor or a memory controller. The bus may range in size from a single signal line to a collection of complex signal line structures. The one or more integrated circuit(s) 14 on each module may be memory device(s) or logic device(s).
The increasing demand for data bandwidth from contemporary bus systems drives the development of impedance controlled buses within such systems. That is, increasing bus system clock speeds require carefully controlled signal line impedances in order to effectively communicate data and control information. At contemporary clock speeds, which already range above several hundred MHz, impedance mismatches on the bus will create unwanted signal reflections which act as noise signals on the bus. Recognizing the need to balance signal line impedances, conventional bus systems terminate the bus in a characteristic impedance 15.
Data and control signals traversing the bus from controller 12 to termination impedance 15 travel the signal path 16 shown in FIG. 1A. Of note, some portions of the signal path pass through the several connectors 11 and other portions of the path pass through the motherboard 10. The transmission performance of such a "mixed" signal path has generally been acceptable in bus systems running a relatively lower frequencies. However, the transmission performance of this type of signal path has proved increasingly inadequate as bus system operating at higher frequencies.
In theory, the composition of the motherboard and the connectors mounted on the motherboard, as well as the signal line traces forming the bus, should produce a consistent impedance matched to termination impedance 15. Actual practice is, however, far from theory. The motherboard is often manufactured by a different entity than the one manufacturing connectors 11 or modules 13. In fact, the printed circuit boards (PCBs) commonly used as motherboards are notoriously variable in their final composition and implementation, and therefore their effective impedance. Further, motherboard impedances tend to vary from unit to unit depending on actual finished trace width, dielectric thickness and composition. As a result, signal path 16 shown in FIG. 1A often suffers from multiple impedance discontinuities caused by the signal path transitions from motherboard-to-connector, and from connector-to-motherboard.